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United States Patent |
5,602,627
|
Kurokawa
|
February 11, 1997
|
Electrifying roller, roller electrifying apparatus using the same, and
image forming apparatus using the same
Abstract
There is provided by the present invention an electrifying roller having a
roller layer having at least two layers of an elastic layer provided on a
peripheral surface of core metal and a surface layer covering the elastic
layer, wherein a slope (.DELTA.I/.DELTA.V) of the V-I characteristics of
the roller layer is 1 or less, the electrifying roller is rotated in
contact with the light-sensing drum, a voltage is loaded from a power
supply unit to the core metal of the electrifying roller, and a surface of
the light-sensing drum is electrified to a surface potential (Vs).
Inventors:
|
Kurokawa; Junji (Yokohama, JP)
|
Assignee:
|
Ricoh Company, Ltd. (Tokyo, JP)
|
Appl. No.:
|
539214 |
Filed:
|
October 4, 1995 |
Foreign Application Priority Data
| Oct 05, 1994[JP] | 6-241630 |
| Nov 30, 1994[JP] | 6-297008 |
| Dec 13, 1994[JP] | 6-309281 |
| Sep 25, 1995[JP] | 7-245929 |
Current U.S. Class: |
399/176; 361/225; 361/230 |
Intern'l Class: |
G03G 015/02 |
Field of Search: |
355/219
430/902
361/225,230,235
|
References Cited
U.S. Patent Documents
5253022 | Oct., 1993 | Takeuchi et al. | 355/274.
|
5272505 | Dec., 1993 | Shishido et al. | 355/219.
|
5287146 | Feb., 1994 | Uno et al. | 355/219.
|
5321471 | Jun., 1994 | Ito et al. | 355/219.
|
5497219 | Mar., 1996 | Kurokawa et al. | 355/219.
|
Foreign Patent Documents |
0534437 | Mar., 1993 | EP | 355/219.
|
0579499 | Jan., 1994 | EP | 355/219.
|
63-149668 | Jun., 1988 | JP.
| |
1-142569 | Jun., 1989 | JP | 355/219.
|
1-210973 | Aug., 1989 | JP | 355/219.
|
2-198468 | Aug., 1990 | JP.
| |
3-123377 | May., 1991 | JP.
| |
3-196067 | Aug., 1991 | JP.
| |
4-138477 | May., 1992 | JP | 355/219.
|
4-333853 | Nov., 1992 | JP.
| |
4-347874 | Dec., 1992 | JP | 355/219.
|
5-16033 | Mar., 1993 | JP.
| |
5-80637 | Apr., 1993 | JP.
| |
5-307315 | Nov., 1993 | JP | 355/219.
|
6-003928 | Jan., 1994 | JP | 355/219.
|
6-35292 | Feb., 1994 | JP | 355/219.
|
Primary Examiner: Smith; Matthew S.
Attorney, Agent or Firm: Lowe, Price, LeBlanc & Becker
Claims
What is claimed is:
1. An electrifying roller comprising a metal core and a roller layer
provided on a peripheral surface of the metal core, said roller layer
comprising at least an elastic layer and a surface layer covering a
surface of said elastic layer, wherein a slope (.DELTA.I/.DELTA.V) of the
V-I characteristic curve of said roller layer, when expressed on
logarithmic paper, is 1 or less.
2. An electrifying roller comprising a metal core and a roller layer
provided around the metal core, said roller layer comprising at least an
elastic layer and a surface layer covering a surface of said elastic
layer, wherein said elastic layer has an electric resistance in a range
from 10.sup.7 to 10.sup.9 .OMEGA..multidot.cm and at the same time a slope
(.DELTA.I/.DELTA.V) of the V-I characteristic curve of said roller layer,
when expressed on logarithmic paper, is 1 or less.
3. A roller electrifying apparatus having an electrifying roller comprising
a metal core, a roller layer on a peripheral surface of the metal core,
said roller layer comprising at least an elastic layer and a surface layer
covering said elastic layer, and a power supply unit for loading a voltage
to the metal core of said electrifying roller, wherein the voltage loaded
to said metal core is a DC constant voltage of 1.6 KV or more with
positive or negative polarity, wherein in said electrifying roller a slope
(.DELTA.I/.DELTA.V) of the V-I characteristic curve of said roller layer,
when expressed on logarithmic paper, is 1 or less.
4. A roller electrifying apparatus having an electrifying roller comprising
a metal core and a roller layer provided on a peripheral surface of the
metal core, said roller layer comprising at least an elastic layer and a
surface layer covering said elastic layer, said electrifying roller having
an electric resistance in a range from 10.sup.7 to 10.sup.9 .OMEGA.cm, and
a power supply unit for loading a voltage to the metal core of said
electrifying roller, wherein the voltage loaded to said metal core is a DC
constant voltage of 1.6 KV or more with positive or negative polarity,
wherein in said electrifying roller a slope (.DELTA.I/.DELTA.V) of the V-I
characteristic curve of said roller layer, when expressed on logarithmic
paper, is 1 or less.
5. An image forming apparatus comprising at least a light-sensing drum, a
rotary electrifying roller which rotates in contact with said
light-sensing drum, an exposure means for projecting light to a surface of
the light-sensing drum electrified by said electrifying roller, and a
developing means for visualizing a latent image formed by said exposure
means, wherein in said electrifying roller comprises a roller layer and
has a slope (.DELTA.I/.DELTA.V) of V-I characteristic curve of the roller
layer, when expressed on logarithmic paper, is 1 or less.
6. An image forming apparatus according to claim 5, wherein a surface
electric potential of said light-sensing drum is electrified to 850 V or
more with positive or negative polarity.
7. An image forming apparatus comprising at least a light-sensing drum, a
rotary electrifying roller, having a roller layer comprising an elastic
layer, which rotates in contact with said light-sensing drum, an exposure
means for projecting light to a surface of the light-sensing drum
electrified by said electrifying roller, and a developing means for
visualizing a latent image formed by said exposure means, wherein an
electric resistance of at least the elastic layer of said electrifying
roller is in a range from 10.sup.7 to 10.sup.9 .OMEGA.cm and said
electrifying roller has a slope (.DELTA.I/.DELTA.V) of 1 or less when the
V-I characteristic curve of the roller layer is expressed on logarithmic
paper.
8. An image forming apparatus according to claim 7, wherein a surface
electric potential of said light-sensing drum is electrified to 850 V or
more with positive or negative polarity.
9. An electrifying roller comprising a metal core and a roller layer
provided on a peripheral surface of the metal core, said roller layer
comprising at least an elastic layer and a surface layer covering said
elastic layer, wherein, assuming that a current value when a DC voltage
V.sub.1 tied to the electrifying roller is 10 V is I.sub.1 .mu.A and a
current value when a DC voltage V.sub.2 tied to the electrifying roller is
100 V is I.sub.2 .mu.A, the V-I characteristics of said roller layer
satisfy the following expression;
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2.
10. An electrifying roller comprising a metal core and a roller layer
provided on the metal core, comprising at least an elastic layer and a
surface layer covering a surface of said elastic layer, wherein an
electric resistance of said elastic layer is in a range from 10.sup.7 to
10.sup.9 .OMEGA..multidot.cm and, assuming that a current value when a DC
voltage V.sub.1 tied to the electrifying roller is 10 V is I.sub.1 .mu.A
and a current value when a DC voltage is V.sub.2 tied to the electrifying
roller is 100 V is I.sub.2 .mu.A, the V-I characteristics of said roller
layer is expressed by the following expression;
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2.
11. An image forming apparatus comprising at least a light-sensing body, an
electrifying roller which rotates in contact with said light-sensing body,
an exposure means for projecting light to a surface of the light-sensing
body electrified by said electrifying roller, and a developing means for
visualizing a latent image formed by said exposure means, wherein,
assuming that a current value when a DC voltage V.sub.1 tied to the
electrifying roller is 10 V is I.sub.1 .mu.A and a current value when a DC
voltage is V.sub.2 tied to the electrifying roller is 100 V is I.sub.2
.mu.A, the V-I characteristics of said roller layer is expressed by the
following expression;
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2.
12. An image forming apparatus comprising at least a light-sensing body, an
electrifying roller, having a roller layer comprising an elastic layer,
which rotates in contact with said light-sensing body, an exposure means
for projecting light to a surface of the light-sensing body electrified by
said electrifying roller, and a developing means for visualizing a latent
image formed by said exposure means, wherein the elastic layer of said
electrifying roller has an electric resistance in a range from 10.sup.7 to
10.sup.9 .OMEGA.cm, and, assuming that a current value when a DC voltage
V.sub.1 tied to the electrifying roller is 10 V is I.sub.1 .mu.A and a
current value when a DC voltage is V.sub.2 tied to the electrifying roller
is 100 V is I.sub.2 .mu.A, the V-I characteristics of said roller layer is
expressed by the following expression;
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2.
13.
13. An image forming apparatus comprising at least a light-sensitive body,
an electrifying roller, having a roller layer, which rotates in contact
with said light-sensing body, an exposure means for projecting light to a
surface of said light-sensing body electrified by said electrifying
roller, and a developing means for visualizing a latent image formed by
said exposure means, wherein, assuming that a current value when a DC
voltage V.sub.1 tied to the electrifying roller is 10 V is I.sub.1 .mu.A
and a current value when a DC voltage is V.sub.2 tied to the electrifying
roller is 100 V is I.sub.2 .mu.A, the V-I characteristics of the roller
layer in said electrifying roller is expressed by the following
expression;
(log I.sub.2 -log I.sub.2)/(log V.sub.2 -log V.sub.1).ltoreq.1.2
said light-sensing body comprises an organic light-sensing body having a
dielectric thickness (D=d/.epsilon.) of 7.5 or more, and a surface
electric potential of said light-sensing body is electrified to 850 V or
more with negative polarity.
14. An image forming apparatus comprising at least a light-sensitive body,
an electrifying roller, having a roller layer, which rotates in contact
with said light-sensing body, an exposure means for projecting light to a
surface of said light-sensing body electrified by said electrifying
roller, and a developing means for visualizing a latent image formed by
said exposure means, wherein an electric resistance of the elastic layer
of said electrifying roller is in a range from 10.sup.7 to 10.sup.9
.OMEGA.cm, and assuming that a current value when a DC voltage V.sub.1
tied to the electrifying roller is 10 V is I.sub.1 .mu.A and a current
value when a DC voltage is V.sub.2 tied to the electrifying roller is 100
V is I.sub.2 .mu.A, the V-I characteristics of the roller layer of said
electrifying roller is expressed by the following expression;
(log I.sub.2 -log I.sub.2)/(log V.sub.2 -log V.sub.1).ltoreq.1.2,
said light-sensing body comprises an organic light-sensing body having a
dielectric thickness (D=d/.epsilon.) of 7.5 or more, and a surface
electric potential of said light-sensing body is electrified to 850 V or
more with negative polarity.
Description
FIELD OF THE INVENTION
The present invention relates an electrifying roller used in an
electrophotographic apparatus, a roller electrifying apparatus using the
same, and an image forming apparatus using the same, and more particularly
to an electrifying roller used for primary electrification and transfer
electrification in an electrophotographic apparatus, a roller electrifying
apparatus using the same, and an image forming apparatus using the same.
BACKGROUND OF THE INVENTION
Conventionally a method in which a high voltage (DC 6 to 8 KV) is loaded to
a metal wire and electrification is executed by making use of generated
corona has widely been used as an electrifying process in an
electrophotographic process. In the corona discharge system as described
above, however, corona products such as ozone or nitrogen oxide generated
when corona is generated denature a surface of a light-sensing body, and
promote shading or degradation of an image, and contamination of wire
gives bad effects to a quality of an image.
On the other hand, there has been developed and put into practical use a
contact electrifying system in which a voltage is loaded to an
electrifying member in contact with a light-sensing drum for electrifying
a surface of the light-sensing body. This electrifying system has the
advantage that a voltage drop in the power supply unit and a quantity of
generated ozone are relatively small, but the uniformity in
electrification is substantially inferior to that in the corona discharge
system.
To improve the uniformity in electrification, for instance, in Japanese
Patent Laid-Open Publication No. 149668/1988 disclosing the "contact
electrifying method", it is disclosed that the uniformity in
electrification can substantially be improved by superimposing an AC
voltage having an inter-peak voltage which is 2 times or more larger than
that of an electrification start voltage (V th) when a DC voltage is
loaded.
Also for improving the uniformity in electrification, for instance in
Japanese Patent Publication No. 16033/1993 disclosing an "electrifying
apparatus", it is disclosed that uniformity in electrification can
substantially be improved with the electrifying apparatus comprising a
conductive base to which a voltage is loaded, a first resistive layer
provided at a position closer to an electrified body than this conductive
base, and a second resistive layer provided at a position closer to said
electrified body than this first resistive layer and having a larger
volume resistivity than that of the first resistive layer, and having an
area where a distance from said electrified body becomes larger and by
loading a voltage having an inter-peak voltage which is 2 times or more
larger than an electrification start voltage to the electrified body.
However, in the contact electrification method disclosed in Japanese Patent
Laid-Open Publication No. 149668/1991, to superimpose a high AC voltage
having an inter-peak voltage which is 2 times or more larger than an
electrification start voltage (V th) when a DC voltage is loaded, an AC
power supply source different from that for a DC power is required, which
causes increase of the apparatus cost. Furthermore by consuming a quantity
of AC power, there occur various problems such as generation of a large
quantity of ozone or drop in durability of the electrifying roller or the
light-sensing body.
Although these problems can be solved by loading only a DC voltage to the
electrifying roller, but when only a DC voltage is loaded to an
electrifying roller, problems as described below occur.
(1) At first, an electrifying roller was prepared, according to the method
disclosed in Japanese Patent Publication No. 16033/1993, by covering a
metal core rod having a diameter of 8 mm with urethane rubber as an
elastic layer containing carbon dispersed therein and having an electric
resistance of 10.sup.4 .OMEGA.cm and thickness of 4 mm, and then providing
a surface layer having a thickness of 25 mm made from a cellophane sheet
with a volumic resistivity of 10.sup.9 .OMEGA.cm, and only a DC voltage
was loaded, when nonuniformity in electrification was generated.
Nonuniformity was generated when carbon black was dispersed in synthetic
rubber as a material for an elastic layer of the electrifying roller.
Namely nonuniformity in the electrifying roller in this case is generated
because of electric nonuniformity in the elastic layer due to carbon black
dispersement fault in synthetic rubber.
(2) A DC voltage of 1.5 KV with negative polarity was loaded to this
electrifying roller to electrify a light-sensing drum such as an OPC to
(-) 800 V, and the electrified light-sensing drum was used. In this case
an excessive current flew through pin holes in the light-sensing layer,
and a voltage loaded to the electrifying roller dropped, which made it
impossible to electrify the light-sensing drum.
(3) An electrifying roller comprising EPRM with carbon dispersed therein as
an elastic layer having an electric resistance in a range from 10.sup.4 to
10.sup.5 .OMEGA.cm and a thickness of 3 mm, hydrin rubber as a resistive
layer having an electric resistance in a range from 10.sup.7 to 10.sup.9
.OMEGA.cm and a thickness of 100 .mu.m, and carbon-dispersed nylon resin
having an electric resistance in a range from 10.sup.7 to 10.sup.9
.OMEGA.cm and a thickness of 100 .mu.m was used, and only a DC voltage was
loaded, and in this case, because dispersibility of carbon and EPDM was
good, electric uniformity of the elastic layer is improved, but withstand
voltage capability of the roller layer is rather poor, so that leak of
electric charge through pin holes in the light-sensing layer often
occurred.
(4) In the conventional type of elastic layer made of carbon and synthetic
rubber, it is possible to adjust an apparent electric resistance by
changing a quantity of added carbon, but it is difficult to simultaneously
realize appropriate conductivity.
(5) Furthermore, electric uniformity of an elastic layer can be improved by
increasing a quantity of carbon dispersed therein to lower an electric
resistance of the entire layer (to 10.sup.4 .OMEGA.cm), but when used only
with a DC voltage, the withstand voltage capability becomes lower.
SUMMARY OF THE INVENTION
The present invention was made to solve the problems as described above,
and it is an object of the present invention to make it possible to
improve the withstand voltage capability of an electrifying roller even
when electrification is performed by loading only a DC voltage and also to
suppress leak of electric charge through pin holes in a light-sensing
drum.
In an electrifying roller having a roller layer comprising at least two
layers of an elastic layer provided around a peripheral surface of core
metal and a surface layer covering a surface of the elastic layer, if (an
electric layer of the elastic layer is in a range from 10.sup.7 to
10.sup.9 .OMEGA.cm, and at the same time) a slope (.DELTA.I/.DELTA.V) of
the V-I characteristics of the roller layer when expressed on logarithmic
paper is 1 or less, namely assuming that current values to given loaded
voltages V.sub.1, V.sub.2 (0<V.sub.1 <V.sub.2 <2 KV) are I.sub.1, I.sub.2,
by adjusting a value of (log I.sub.2 -log I.sub.1)/(log V.sub.2 -log
V.sub.1) so that the value will not surpass 1, the withstand voltage
capability of the electrifying roller is improved, and the possibility of
charge leak is eliminated.
Furthermore by adjusting an electric resistance of the elastic layer to a
range from 10.sup.7 to 10.sup.9 .OMEGA.cm, the withstand voltage
capability of the electrifying roller is improved, and the possibility of
charge leak is eliminated. And also by loading a DC constant voltage of
1.6 KV or more with positive or negative polarity to the core metal, the
light-sensing drum can be electrified to high electric potential.
Furthermore by adjusting a slope (.DELTA.I/.DELTA.V) of the V-I
characteristics of a roller layer in an electrifying roller when expressed
with logarithmic paper to 1 or below, a light-sensing drum can be
electrified to high electric potential.
Because (at least an elastic layer of the electrifying roller has an
electric resistance in a range from 10.sup.7 to 10.sup.9 .OMEGA.cm, and at
the same time) a slope (.DELTA.I/.DELTA.V) of the V-I characteristics of
the roller layer of the electrifying roller when expressed with
logarithmic paper is 1 or less, the withstand voltage capability of the
electrifying roller is improved, and the possibility of charge leak is
eliminated. Also a voltage loaded to the core metal is a DC constant
voltage of 1.6 KV or more with positive or negative polarity, so that the
light-sensing drum can be electrified to high electric potential.
Furthermore by electrifying surface potential of the light-sensing drum to
850 V or more with positive or negative polarity, allowance is generated
in the bias potential for development.
Furthermore the electrifying roller has a roller layer comprising two
layers of an elastic layer (with an electric resistance in a range from
10.sup.7 to 10.sup.9 .OMEGA.cm) and a surface layer covering a surface of
the elastic layer, and the V-I characteristics of the roller layer
satisfies the following expression:
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2
assuming that a current value when a DC voltage V.sub.1 is 10 V is I.sub.1
.mu.A and a current value when a DC voltage V.sub.2 is 100 V is I.sub.2
.mu.A.
Furthermore image forming is executed with an electrifying roller having a
roller layer comprising two layers of an elastic layer (with an electric
resistance in a range from 10.sup.7 to 10.sup.9 .OMEGA.cm) and a surface
layer covering a surface of the elastic layer in which the V-I
characteristics of the roller layer satisfies the following expression:
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2
assuming that a current value when a DC voltage V.sub.1 is 10 V is I.sub.1
.mu.A and a current value when a DC voltage V.sub.2 is 100 V is I.sub.2
.mu.A.
Also by using an electrifying roller having a roller layer comprising two
layers of an elastic layer (with an electric resistance in a range from
10.sup.7 to 10.sup.9 .OMEGA.cm) and a surface layer covering a surface of
the elastic layer in which the V-I characteristics of the roller layer
satisfies the following expression:
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2
assuming that a current value when a DC voltage V.sub.1 is 10 V is I.sub.1
.mu.A and a current value when a DC voltage V.sub.2 is 100 V is I.sub.2
.mu.A, and also using an organic light-sensing body with the dielectric
thickness (D=d/.epsilon.) of 7.5 or more, image forming is executed by
electrifying surface potential of the light-sensing body to 850 V or more
with negative polarity.
Other objects and features of this invention will become understood from
the following description with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory view showing general configuration of an
electrifying roller and a roller electrifying apparatus using the same;
FIG. 2 is an explanatory view showing the V-I characteristics of an roller
layer of the electrifying roller as well as a method of measurement of
electric resistance of an electrifying roller elastic layer;
FIG. 3 is a graph showing a current-voltage characteristics of the elastic
layer of the electrifying roller; and
FIG. 4 is a configuration view showing general configuration of an image
forming apparatus having the electrifying roller.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Detailed description is made hereinafter for an electrifying roller, a
roller electrifying apparatus using the same, and an image forming
apparatus using the same according to the present invention with reference
to the related drawings each in the order of [Embodiment 1], [Embodiment
2], [Embodiment 3], [Embodiment 4], [Embodiment 5], and [Embodiment 6].
[Embodiment 1]
Description is made for configuration of an electrifying roller and a
roller electrifying apparatus using the same according to Embodiment 1
with reference to FIG. 1. An electrifying roller 101 has a roller layer
105 provided on a peripheral surface of core metal 103 and comprising two
layers of an elastic layer 101a and a surface layer 101b covering a
surface of the elastic layer 101a, and in the electrifying apparatus using
the electrifying roller 101, the electrifying roller 101 is rotated in
contact with a light-sensing drum 102, a voltage is loaded (a load voltage
(Va) is injected) from a power supply unit 104 to core metal 103 of the
electrifying roller 101, and a surface potential (Vs) is generated on a
surface of the light-sensing drum 102.
FIG. 2 is an explanatory view showing a method of measuring the V-I
characteristics of a roller layer 105 of the electrifying roller 101 and
an electric resistance of an elastic layer 101a of the electrifying roller
101. A tin foil electrode 201 having a width of 18 mm is pasted on a
peripheral surface of the electrifying roller 101, a voltage is loaded to
between the tin foil electrode 201 and the core metal 103 of the
electrifying roller 101, and a current (I) generated when the voltage (V)
is loaded is measured.
Then samples of the electrifying roller 101 are prepared. As samples,
samples 1 to 3 and samples for comparison 1 and 2 are prepared.
Sample 1
An elastic layer made of epichlorohydrin having an electric resistance of
2.times.10.sup.8 .OMEGA..multidot.cm and a thickness of 3 mm is provided
on a peripheral surface of core metal with a diameter of 8 mm, and
furthermore a surface layer 101b made of nylon (CM4000) having a thickness
of 5 .mu.m is provided on a peripheral surface of the elastic layer. A
diameter of the roller in this case is 14 mm.
Sample 2
An elastic layer made of epichlorohydrin having an electric resistance of
3.times.10.sup.8 .OMEGA.cm and a thickness of 4 mm is provided on a
peripheral surface of core metal with a diameter of 8 mm, and furthermore
a surface layer 101b made of hydrin rubber/fluorine resin admixture having
a thickness of 7 .mu.m is provided on a peripheral surface of the elastic
layer. A diameter of the roller in this case is 16 mm.
Sample 3
An elastic layer made of urethane rubber/alkali metallic
salt/carbon-dispersed system having an electric resistance of
3.5.times.10.sup.7 .OMEGA.cm and a thickness of 3 mm is provided on a
peripheral surface of core metal with a diameter of 6 mm, and furthermore
a surface layer 101b made of nylon (CM4000) having a thickness of 5 .mu.m
is provided on a peripheral surface of the elastic layer. A diameter of
the roller in this case is 12 mm.
Then samples for comparison are prepared. It should be noted that an
electrifying roller similar to a conventional type of electrifying roller
to which both AC and DC voltages are loaded is used as a sample for
comparison.
Sample for comparison 1
A surface layer made of cellophane (with an electric resistance of
1.times.10.sup.4 .OMEGA.cm) is provided on an elastic layer made of
urethane rubber/carbon dispersed system. A diameter of the roller in this
case is 16 mm.
Sample for comparison 2
A resistive layer made of hydrin rubber (with an electric resistance in a
range from 10.sup.7 to 10.sup.9 .OMEGA.cm and a thickness thereof of 10
mm) and a surface layer made of nylon/carbon (with an electric resistance
in a range from 10.sup.7 to 10.sup.10 .OMEGA.cm and a thickness thereof of
10 mm) are provided on an elastic layer made of EPDM/carbon dispersed
system (with an electric resistance in a range from 10.sup.4 to 10.sup.5
.OMEGA..multidot.cm and a thickness thereof of 3 mm). A diameter of the
roller in this case is 16 mm.
Then electrifying rollers incorporating the samples 1, 2, and 3, and also
samples for comparison 1 and 2 described above each were prepared as trial
rollers 1, 2, 3, 4, and 5 respectively, and the trial rollers 1, 2, 3, 4,
and 5 were used in the electrifying roller apparatus shown in FIG. 1, and
the electrifying characteristics of the light-sensing body in each case
was evaluated.
In the electrifying roller apparatus, it is assumed that a load voltage Va
is (-) 1.5 KV, and a linear velocity V of the light-sensing drum 102 is
120 mm/sec.
In the trial rollers 4 and 5, electrified potential Vs was in a range from
800 V to 860 V, but the electrified potential (Vs) was not stable and
largely dispersed, and also a leak through pin-holes of the OPC
light-sensing drum occurred quite often.
On the contrary, in the trial rollers 1, 2, and 3, electrified potential Vs
was in a range from 750 V to 800 V, somewhat lower as compared to that in
the trial rollers 4 and 5, but uniformity in electrification thereof was
excellent, and a leak of electric charge through pin-holes of the OPC
light-sensing drum 102 did not occur.
Then the V-I characteristics of the trial rollers 1 to 5 each was measured
by using the method of measuring an electric resistance of the elastic
layer of electrifying roller shown in FIG. 2, and the result is shown in
FIG. 3. FIG. 3 is a graph showing a current-voltage characteristics of the
roller layer of electrifying roller. As shown in FIG. 3, in the trial
rollers 1, 2, and 3, an electric resistance of the roller layer is larger
as compared to that in the trial rollers 4 and 5, and the dependency on
the current (I) flowing through the roller layer on a voltage is small.
It should be noted that straight lines shown in FIG. 3 each indicate the
trial rollers respectively as follows;
______________________________________
Trial roller 1 .largecircle. -- .largecircle.
Trial roller 2 .DELTA. -- .DELTA.
Trial roller 3 .quadrature. -- .quadrature.
Trial roller 4 .circle-solid. -- .circle-solid.
Trial roller 5 .tangle-solidup. -- .tangle-solidup.
______________________________________
Also with reference to FIG. 3, a result of the test for the trial rollers
1, 2, and 3 indicates that a slope (.DELTA.I/.DELTA.V) of the V-I
characteristics of the roller layer when expressed on logarithmic paper is
1 or less, namely, if current values are I.sub.1 and I.sub.2 to given
loaded voltage V.sub.1 and V.sub.2 respectively (it should be noted that,
0<V.sub.1 <V.sub.2 <2 KV), a value of (log I.sub.2 -log I.sub.1)/(log
V.sub.2 -log V.sub.1) is not more than 1.
With Embodiment 1 as described above, by adjusting an electric resistance
of the elastic layer of the electrifying roller to a range from 10.sup.7
to 10.sup.9 .OMEGA.cm, the withstand voltage capability can be improved,
namely the uniformity in electrification can be improved, and the
possibility of electric charge leak due to pin-holes of the light-sensing
drum 102 is eliminated.
As clearly shown in FIG. 3, in the electrifying roller insuring uniformity
in electrification, the slope (.DELTA.I/.DELTA.V) of the V-I
characteristics of the roller layer when expressed on logarithmic paper is
1 or less. In other words, as shown in Embodiment 1, in an electrifying
roller satisfying conditions that electric resistance of the elastic layer
of the electric roller is in a range from 10.sup.7 to 10.sup.9 .OMEGA.cm,
and the slope (.DELTA.I/.DELTA.V) of the V-I characteristics of the roller
layer in the electrifying roller when expressed by logarithmic paper is 1
or less, uniformity of electrification is improved, and generation of a
leak due to pin-holes of the light-sensing drum can be avoided.
[Embodiment 2]
In Embodiment 2, by using the samples 1 to 3 which are electrifying rollers
like those in Embodiment 1 and also by using the apparatus shown in FIG.
1, performance of an electrifying roller is checked only by changing the
light-sensing drum 102. It is assumed in configuration shown in FIG. 1
that the light-sensing drum 102 is rotated at a linear velocity V of 180
mm/sec.
The following components are used as the light-sensing drum 102.
(1) For electrification with positive polarity: a light-sensing body made
of Se system
(an overcoat layer made of St-MA denatured urethane resin/SiO.sub.2 having
a thickness of 3 .mu.m covering AS.sub.2 Se.sub.3 layer having a thickness
of 50 .mu.m)
(2) For electrification with negative polarity: a light-sensing drum of OPC
system
(a CGL/CTL laminated light-sensing body having a thickness of 25 .mu.m)
Then in Embodiment 2, using the samples 1 to 3 used in Embodiment 1 and the
light-sensing drums 102 (1) and (2), electrification was carried out with
a load voltage (a DC constant voltage) Va of .+-.1.65 KV, and the stable
electrification having an electrifying potential Vs of (.+-.) 820 V to 900
V could be obtained.
With Embodiment 2 as described above, in the roller electrifying apparatus
using the electrifying roller with high withstand voltage capability used
in Embodiment 1 and the image forming apparatus using the same, a high DC
voltage can be loaded to the core metal of electrifying roller, so that
the light-sensing drum 102 can be electrified to a high electric
potential, and in addition the electrifying potential can be stabilized.
[Embodiment 3]
Embodiment 3 of the present invention is a case where the electrifying
roller according to Embodiment 1 and Embodiment 2 and a roller
electrifying roller using the same are applied to an image forming
apparatus, and next description is made for Embodiment 3 with reference to
FIG. 4. It is assumed in the following description that the samples 1 to
3, which are electrifying rollers like those in Embodiment 1 and the
light-sensing drums 102 (1), (2) like those in Embodiment 2 are used.
FIG. 4 is a block diagram illustrating the image forming apparatus
according to Embodiment 3. This image forming apparatus comprises an
electrifying roller 101 provided on a peripheral surface of the
drum-shaped light-sensing drum 102, an image exposure device (not shown
herein), a developing device 401, a transfer electrifying belt 402, a
cleaning device 403, and a pre-exposure device 404. It should be noted
that in this figure, the reference numeral 405 indicates a light for
exposure emitted from the image exposure device.
In the image forming apparatus shown in FIG. 4, the samples 1 to 3 are
installed in the electrifying roller 101 and the light-sensing drums (1),
(2) in the light-sensing drum 102 in various types of combination
respectively, and measurement is carried out at a linear velocity V of the
light-sensing drum of 210 mm/sec and with a loaded voltage Va of .+-.1.7
KV.
The measurement method is as shown in FIG. 1. As a result of measurement
under the conditions described above, an electrified potential Vs of
.+-.850 to 950 V was obtained. Also in any combination of the samples 1 to
3 and light-sensing drums (1), (2), an image with high density was
obtained, and image fault due to nonuniformity in electrification or leak
of electric charge did not occur at all.
With Embodiment 3 as described above, the light-sensing drum 102 can be
electrified to a high electric potential with a load voltage (Va), so that
allowance is generated in bias potential for develop in the image forming
apparatus and, eve, if high speed system PCC is used in the image forming
apparatus, a high density and high quality image without background
contamination.
[Embodiment 4]
Then a sample of the electrifying roller 101 was prepared. As samples,
samples 1 to 6 was prepared with those for comparison 1, 2.
Sample 1
An epichlorohydrin elastic layer 101a having an electric resistance of
2.times.10.sup.8 .OMEGA.cm and a thickness of 2 mm is provided on a
peripheral surface of core metal with a diameter of 8 mm, and furthermore
a nylon (CM4000) surface layer 101b having a thickness of 5 .mu.m is
provided on the peripheral surface of the elastic layer 101a. A diameter
of the roller in this case is 12 mm.
Sample 2
An epichlorohydrin elastic layer 101a having an electric resistance of
3.times.10.sup.8 .OMEGA.cm and a thickness of 3 mm is provided on a
peripheral surface of core metal with a diameter of 8 mm, and furthermore
a surface layer 101b made of hydrin rubber/fluorine resin admixture
(mixing ratio of 1/3.5) and having a thickness of 7 .mu.m is provided a
peripheral surface of the elastic layer. A diameter of the roller in this
case is 14 mm.
Sample 3
An elastic layer 101a made of a material in which urethane, alkali metal
salt, and carbon are dispersed and having an electric resistance of
3.5.times.10.sup.7 .OMEGA.cm as well as a thickness of 3 mm is provided on
a peripheral surface of core metal having a diameter of 6 mm, and
furthermore a nylon (CM4000) surface layer 101b having a thickness of 5
.mu.m is provided on a peripheral surface of the elastic layer. A diameter
of the roller in this case is 12 mm.
Sample 4
An elastic layer 101a made of urethane rubber/alkali metal salt and having
an electric resistance of 10.sup.9 .OMEGA.cm and a thickness of 3 mm is
provided on a peripheral surface of core metal having a diameter of 6 mm,
and furthermore a carbon-dispersed nylon (CM8000) surface layer 101b
having a thickness of 20 .mu.m is provided on a peripheral surface of the
elastic layer. A diameter of the roller in this case is 12 mm.
Sample 5
An epichlorohydrin elastic layer 101a having an electric resistance of
2.times.10.sup.8 .OMEGA.cm and a thickness of 3 mm is provided on a
peripheral surface of core metal having a diameter of 8 mm, and
furthermore a carbon-dispersed fluorine resin surface layer 101b having a
thickness of 20 .mu.m is provided on a peripheral surface of the elastic
layer. A diameter of the roller in this case is 14 mm.
Sample 6
A epichlorohydrin elastic layer 101a having an electric resistance of
1.5.times.10.sup.8 .OMEGA.cm and a thickness of 3 mm is provided on a
peripheral surface of core metal having a diameter of 8 mm, and
furthermore a hydrin rubber/fluorine resin admixture (mixing ratio: 1/1.7)
surface layer 101b having a thickness of 30 .mu.m is provided on a
peripheral surface of the elastic layer. A diameter of the roller in this
case is 14 mm.
Then samples for comparison are prepared. It should be noted that the
samples for comparison are similar to electrifying rollers based on the
conventional technology in which both AC and DC voltages are loaded.
Sample 1 for comparison
An elastic layer (having an electric resistance of 1.times.10.sup.4
.OMEGA.cm) made of urethane rubber with carbon dispersed therein and a
surface layer made of cellophane are provided. A diameter of the roller in
this case is 16 mm.
Sample 2 for comparison
An elastic layer (having an electric resistance in a range from 10.sup.4 to
10.sup.5 .OMEGA.cm) made of EPDM with carbon dispersed therein, a hydrin
resistive layer (having an electric resistance in a range from 10.sup.7 to
10.sup.9 .OMEGA.cm), and furthermore a nylon/carbon surface layer are
provided. A diameter of the diameter in this case is 16 mm.
Then evaluation was made for the electrifying characteristics of the
light-sensing drum 102 in a case where the samples above were applied to
the roller electrifying apparatus shown in FIG. 1. A voltage Va loaded to
the roller electrifying apparatus was (-) 1.5 KV, and a linear velocity V
of the light-sensing drum 102 was 120 mm/sec.
In the samples 5,6 and those for comparison 1,2, the electrified potential
Vs was in a range from 800 to 900 V, but the electrified potential was not
stable with large dispersion, and also leak of electric charge often
occurred through pinholes of the OPC light-sensing drum 102.
In contrast, in the samples 1 to 4, the electrified potential Vs was in a
range from 750 to 800 V, slightly lower, but uniformity in electrification
was high, and leak of electric charge through pin-holes of the OPC
light-sensing drum 102 did not occur.
A result of measurement of the V-I characteristics of a roller layer in
each sample and a result of evaluation of the electrifying characteristics
are shown in Table 1. An electric resistance of the elastic layer 101a of
the electrifying roller 101 was measured for each sample by using the
measuring device shown in FIG. 2.
__________________________________________________________________________
Electric Resistance
V-I Characteristics Result of
of Elastic Layer
of Roller Layer Evaluation of
Electrifying
of Roller V.sub.1 = 10 V
V.sub.2 = 100 V
logI.sub.2 - logI.sub.1
Electrifying
Roller (.OMEGA. .multidot. cm)
I.sub.1 (.mu.A)
I.sub.2 (.mu.A)
logV.sub.2 - logV.sub.1
Characteristics
__________________________________________________________________________
Sample 1
2 .times. 10.sup.8
.OMEGA. .multidot. cm
1.7 .mu.A
13 .mu.A
0.88 .largecircle.
Sample 2
3 .times. 10.sup.8
1.4 9 0.81 .largecircle.
Sample 3
##STR1## 2.9 46 1.20 .largecircle.
Sample 4
10.sup.9 1.1 12 1.04 .largecircle.
Sample 5
2 .times. 10.sup.8
3.5 105 1.48 X
Sample 6
1.5 .times. 10.sup.8
1.6 26 1.21 X
Sample for
1 .times. 10.sup.4
5.5 115 1.32 X
Comparison
Sample for
10.sup.4-5 /10.sup.7-9
37 610 1.22 X
Comparison 2
__________________________________________________________________________
As clearly shown in Table 1, in the electrifying rollers with excellent
electrifying characteristics, the V-I characteristics of the roller layer
satisfies the condition expressed by the expression of (log I.sub.2 -log
I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2 assuming that a current
value in the state of V.sub.1 =10 V is I.sub.1 .mu.A and a current value
is the state of V.sub.2 =100 V is I.sub.2 .mu.A. In other words, in an
electrifying roller in which an electric resistance of the elastic layer
is in a range from 10.sup.7 to 10.sup.9 .OMEGA.cm and a slope of the V-I
characteristics of the roller layer expressed by the equation of (log
I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1) is 1.2 or less,
uniformity in electrification is high, and generation of electric charge
leak through pin holes of the light-sensing drum can be suppressed.
As described above, in Embodiment 4, an electric resistance of the elastic
layer 101a is in a range from 10.sup.7 to 10.sup.9 .OMEGA.cm, and the V-I
characteristics of the roller layer 105 satisfies the condition expressed
by the expression of (log I.sub.2 -log I.sub.1)/(log V.sub.2 -log
V.sub.1).ltoreq.1.2, so that, even if electrification is carried out by
loading only a DC voltage to the electrifying roller 101, the withstand
voltage capability of the electrifying roller 101 can be improved and leak
of electric charge through pin-holes of the light-sensing body can be
suppressed.
[Embodiment 5]
FIG. 4 is a block diagram illustrating an image forming apparatus according
to Embodiment 5 of the present invention. This image forming apparatus is
a system in which the electrifying roller (Samples 1 to 4) according to
Embodiment 4 is applied, and as shown in this figure, provided on a
peripheral surface of the drum-shaped light-sensing drum 102 are an
electrifying roller 101, an image exposure device (not shown), a
developing device 401, a transfer belts 402, a cleaning device 403, and a
pre-exposure device 404. It should be noted that the reference numeral 405
indicates light for exposure emitted from the image exposure device.
With the configuration as described above, a linear velocity V of the
light-sensing drum 102 was set to 180 mm/sec, and electrification was
carried out with a loaded voltage Va of (-) 1.65 KV using the electrifying
roller 101 prepared in Embodiment 4 for forming an image, and as a result
a high quality image was obtained.
As described above, with Embodiment 5, an image forming apparatus by
applying the electrifying roller with excellent withstand voltage
capability (Samples 1 to 4 in Embodiment 4) was constructed, so that a
voltage loaded to a roller can be increased even at a high operating speed
and a high density and high quality image can be obtained.
[Embodiment 6]
In the image forming apparatus shown in FIG. 4, an OPC-based light-sensing
drum having a diameter of 60 mm was used as a light-sensing drum 102. It
is a CGL/CTL laminated light-sensing body with a thickness of 25 .mu.m.
The dielectric thickness D (D=d/.epsilon.) of the light-sensing body is
8.3 (Thickness d: 25 .mu.m, and the specific dielectric constant
.epsilon.: 3). If a layer thickness of the OPC light-sensing body becomes
larger, the electrifying efficiency in electrification of the roller
becomes slightly lower, but when durability of the OPC light-sensing body
is taken into considerations, it is required that D is 8 or more. For this
reason, if high electrified potential is required for obtaining a high
density image, an electrifying roller with high withstand voltage
capability may be used with high voltage to be loaded. Even if any of the
samples 1 to 4 in Embodiment 4 is used as the electrifying roller 101,
always the stable electrified potential Vs of 850 to 950 V and a high
density image could be obtained with the loaded voltage Va of (-) 1.7 KV.
With Embodiment 6, surface potential of an OPC light-sensing body with a
dielectric thickness D of 8 or more is electrified to 850 V or more with
negative polarity, so that allowance is generated in bias potential for
development, and always a high density image without background
contamination can be obtained.
It should be noted that the above description assumes an electrifying
roller having a roller layer consisting of an elastic layer provided on
core metal and a surface layer covering a surface of the elastic layer,
but construction in this embodiment is not limited to that described
above, and the present invention can be applied to an electrifying roller
having a roller layer comprising a single layer or three or more layers.
As described above, with the electrifying roller according to the present
invention, in the electrifying roller having a roller layer provided on a
peripheral surface of a core metal and comprising at least two layers of
an elastic layer and a surface layer covering a surface of the elastic
layer, if (an electric resistance of the elastic layer is in a range from
10.sup.7 to 10.sup.9 .OMEGA.cm, and at the same time) a slope
(.DELTA.I/.DELTA.V) of the V-I characteristics of the roller layer when
expressed on logarithmic paper is 1 or less, namely, if a current value is
I.sub.1, I.sub.2 to a given loaded voltage V.sub.1, V.sub.2 respectively
(it should be noted that, 0<V.sub.1 <V.sub.2 <2 KV), a value of (log
I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1) is not more than 1, and
for this reason even in a case where the electrifying roller is
electrified by loading only a DC voltage thereto, the withstand voltage
capability of the electrifying roller can be improved, and at the same
time a leak of electric charge due to pin-holes of the light-sensing drum
can be avoided.
In the roller electrifying apparatus according to the present invention,
(assuming that electric resistance of the elastic layer is in a range from
10.sup.7 to 10.sup.9 .OMEGA.cm, and) a voltage loaded to a core metal is
set to a DC constant voltage of 1.6 KV or more with positive or negative
polarity, so that even in a case where an electrifying roller is
electrified by loading only a DC voltage thereto, the withstand voltage
capability of an electrifying roller can be improved, and at the same time
leak of electric charge due to pin-holes of a light-sensing drum can be
avoided. Also the light-sensing drum can be electrified to a high electric
potential.
In the roller electrifying apparatus according to the present invention, a
slope (.DELTA.I/.DELTA.V) of the V-I characteristics of the roller layer
of an electrifying roller when expressed on logarithmic paper is set to 1
or less, so that the light-sensing drum can be electrified to a further
higher electric potential.
In the image forming apparatus according to the present invention, (at
least an electric resistance of the elastic layer of the electrifying
roller is in a range from 10.sup.7 to 10.sup.9 .OMEGA.cm, and), a slope
(.DELTA.I/.DELTA.V) of the V-I characteristics of the roller layer of the
electrifying roller when expressed on logarithmic paper is 1 or less, so
that even in a case where an electrifying roller is electrified by loading
only a DC voltage thereto, the withstand voltage capability of an
electrifying roller can be improved, and at the same time leak of charge
due to pin-holes of the light-sensing drum can be avoided.
In the image forming apparatus according to the present invention, a
surface electric potential of the light-sensing drum is electrified to 850
V or more with positive or negative polarity, so that even in a case where
an electrifying roller is electrified by loading only a DC voltage, the
withstand voltage capability of an electrifying roller can be improved,
and at the same time leak of electric charge due to pin-holes of the
light-sensing drum can be avoided, and allowance in bias electric
potential for development is generated.
The electrifying roller according to the present invention has a roller
layer comprising two layers of an elastic layer (with an electric
resistance in a range from 10.sup.7 to 10.sup.9 .OMEGA..multidot.cm) and a
surface layer covering a surface of the elastic layer, and assuming that a
current value when a DC voltage V.sub.1 is 10 V is I.sub.1 .mu.A and a
current value when a DC voltage V.sub.2 is 100 V is I.sub.2 .mu.A, the
electrifying roller is formed so that the V-I characteristics of the
roller layer satisfies the following expression;
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2
and for this reason, even in a case where the electrifying roller is
electrified by loading only a DC voltage, the withstand voltage capability
of an electrifying roller can be improved, and at the same time leak of
electric charge due to pin-holes of the light-sensing drum can be avoided.
The image forming apparatus according to the present invention has a roller
layer comprising two layers of an elastic layer (with an electric
resistance in a range from 10.sup.7 to 10.sup.9 .OMEGA..multidot.cm) and a
surface layer covering a surface of the elastic layer, and image forming
is executed by using an electrifying roller formed so that the V-I
characteristics of the roller layer satisfies the condition expressed by
the following expression;
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2
assuming that a current value when a DC voltage V.sub.1 is 10 V is I.sub.1
.mu.A and a current value when a DC voltage V.sub.2 is 100 V is I.sub.2
.mu.A, and for this reason, even in a case where the electrifying roller
is electrified by loading only a DC voltage, the withstand voltage
capability of an electrifying roller can be improved, and at the same time
leak of electric charge due to pin-holes of the light-sensing drum can be
avoided.
The image forming apparatus according to the present invention has a roller
layer comprising two layers of an elastic layer (of which electric
resistance is in a range from 10.sup.7 to 10.sup.9 .OMEGA..multidot.cm)
and a surface layer covering the elastic layer, and image forming is
executed using an electrifying roller formed so that the V-I
characteristics of the roller layer satisfies the condition expressed by
the following equation;
(log I.sub.2 -log I.sub.1)/(log V.sub.2 -log V.sub.1).ltoreq.1.2
also by using an organic light-sensing body having a dielectric thickness
(D=d/.epsilon.) of 7.5 or more, and by electrifying a surface electric
potential of the light-sensing body to 850 V or more with negative
polarity, so that even in a case where an electrifying roller is
electrified by loading only a DC voltage, the withstand voltage capability
of an electrifying roller can be improved, and at the same time a leak of
charge due to a pin-hole of a light-sensing drum can be avoided.
Although the invention has been described with respect to a specific
embodiment for a complete and clear disclosure, the appended claims are
not to be thus limited but are to be construed as embodying all
modifications and alternative constructions that may occur to one skilled
in the art which fairly fall within the basic teaching herein set forth.
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